ng add @angular/pwa cannot find AppModule if imported through index.ts

Start in packages/schematics/angular/utility/ng-ast-utils.ts at findBootstrapModulePath, then follow its use in packages/schematics/angular/service-worker/index.ts by updateAppModule. Reproduce with an AppModule re-exported through app/index.ts and ng add @angular/pwa; done means the indirect import resolves to the real module file instead of attempting to update /src/app.ts.

Bug Report or Feature Request (mark with an x)

- [x] bug report -> please search issues before submitting
- [ ] feature request

Area

- [ ] devkit
- [x] schematics

Versions

$ node --version
v8.11.2

$ npm --version
5.6.0

Repro steps

• Create an Angular 6 application
• If not present, create a index.ts in the App module folder with at least the following content:

export * from './app.module';

• In the main.ts, import the App module indirectly by using its parent folder:

import './polyfills.ts';

import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { enableProdMode } from '@angular/core';
import { environment } from './environments/environment';
import { AppModule } from './app'; // works because ./app/index.ts exports AppModule

if (environment.production) {
    enableProdMode();
}

platformBrowserDynamic().bootstrapModule(AppModule);

• Now use angular CLI to add PWA

$ ng add @angular/pwa --project <your-project-name-from-angular-json>

The log given by the failure

Installing packages for tooling via npm.

+ @angular/pwa@0.6.8
updated 1 package in 11.487s
Installed packages for tooling via npm.
Could not read file (/src/app.ts).

Desired functionality

Make PWA install work even when importing the AppModule indirectly (through an index.ts).

To be more accurate, the findBootstrapModulePath function from ng-ast-utils.d.ts should properly identify the AppModule path in this setup.
https://github.com/angular/angular-cli/blob/44086c60ff1d6c26d30850bef125120f6c498ac1/packages/schematics/angular/utility/ng-ast-utils.ts#L49

This method is called by updateAppModule from https://github.com/angular/angular-cli/blob/8ce5ef48b81af484c37123d36422b3c58ddc1ffd/packages/schematics/angular/service-worker/index.ts#L99

The failure occurs when trying to update the content of a file which does not exists. Checking the file exists and displaying a better message would also help.

Mention any other details that might be useful

The issue was encountered when attempting to add PWA to our NGXP Seed web side.

$ git clone https://github.com/Monogramm/ngxp-seed.git
$ git checkout develop
$ ng add @angular/pwa --project web

Since we managed to find out the root cause, the workaround of using the complete path will be used for now.